Abstract: The advantages of millimeter wave technology and its applications in radar systems and communications are presented in this paper. In addition, the development and recent trends are introduced, and the challenges of achieving and leveraging the technologies are particularly analyzed. With respect to various applications and technology features, four technological roadmaps of millimeter wave phased array antenna meeting the demands of various applications are explicitly illustrated. The key technologies of architecture, radiator, device and package for millimeter wave phased array system are also shown in detail. As a whole, the purpose of this paper is to scientifically analyze and summarize the technological systems, applications and development trends, providing valuable reference for designing millimeter wave phased array antenna.